Consistent --program-prefix for GNU programs

[Blair Zajac]

Some of our GNU ports use a --program-prefix of gnu:

     findutils
     gnutar
     gnumake-devel
     gsed
     indent

while others use g:

     binutils
     coreutils
     diffutils
     gmake
     gpatch
     gtime
     gunits
     gwhich
     libtool
     libtool-devel
     m4

It would be nice to have a MacPorts' standard here and it looks like changing 
the gnu to the g ones would be less work

I'd also like all of these ports to have a variants to disable the 
program-prefix.  Currently, only diffutils has a variant named 'normal', which 
is not a good name in my opinion.  I'd like to see a variant named 
no-program-prefix.

What do people think?

Regards,
Blair